There is a serverconfig.xml inside the server directory where you can set up your server. Every line has a helpful comment after it so you should have no problems making adjustments.
A few of the lines are commented out with <!-- and -->, for example "UserDataFolder". If you want to change those values you have to remove the comment braces.
There is also a slightly more detailed description of how to set up a dedicated server on some steam page, you should be able to find that with a search engine